# [145. Binary Tree Postorder Traversal](https://leetcode.com/problems/binary-tree-postorder-traversal/)

## 题目


Given a binary tree, return the postorder traversal of its nodes' values.



**Example**:

```

Input: [1,null,2,3]
   1
    \
     2
    /
   3

Output: [3,2,1]

```


**Follow up**: Recursive solution is trivial, could you do it iteratively?


 

## 题目大意

后根遍历一颗树。

## 解题思路

递归的实现方法，见代码。





## 代码

```go

package leetcode

/**
 * Definition for a binary tree node.
 * type TreeNode struct {
 *     Val int
 *     Left *TreeNode
 *     Right *TreeNode
 * }
 */
func postorderTraversal(root *TreeNode) []int {
	var result []int
	postorder(root, &result)
	return result
}

func postorder(root *TreeNode, output *[]int) {
	if root != nil {
		postorder(root.Left, output)
		postorder(root.Right, output)
		*output = append(*output, root.Val)
	}
}

```